Some Authentication Studies

In the following sections, an overview of some of the techniques commonly used in food authentication studies is given, along with an explanation as to why a particular technique (or combination of techniques) might be chosen. 

However, it is not just the presence or absence of an element that is useful (as most elements will be present at some concentration), but it is the relative variation in the trace element profile that is the parameter that provides the major discriminatory power. McHard et al. [16] were possibly some of the first researchers to apply a normalization procedure to multielement data in order to maximize the differences between two sets of samples. Their approach, which is now accepted as being a standard tool for use in chemometric investigations, was to identify an element whose concentration was constant, irrespective of the geographical origin of the samples, and then to normalize all other elemental data against it. In McHard s study on fruit juice, they used Zn. The authors of this chapter used Ca in an egg authenticity study, where eggshells were used as the sample matrix (unpublished data) and Mg was used in a study of Welsh onions [14]. 

Crews, C., Hough, R, Godward, J., Brereton, R, Lees, M., Guiet, S., and Winkelmann, W., Study of the main constituents of some authentic hazelnut oils, J. Agric. Food Chem., 53, 4843-4852, 2005. 

Reduction of thiopyrylium salts to 2H- and 4/f-thiopyrans by trichlorosilane and by lithium aluminium hydride has been reported. Addition of organo-metallic reagents to thiopyrylium and selenopyrylium salts, which was (see Volume 2, p. 387) believed to yield thia- and selena-benzenes, has now been shown to give oligomers. Some authentic thia- > and selena-benzenes have been prepared. Nucleophilic addition to, and nitration of, 9-phenyl-selenoxanthylium salts (28) has been studied. 

A number of synthetic methods to prepare all the three main classes of AHLs have appeared in the literature. Initially the methods were developed to prepare the authentic AHLs with defined stereochemistry to confirm the identity of the natural signal molecule. Subsequently, when some of these molecules, e.g. AT-(3-oxododecanoyl)-L-homoserine lactone were found to impact on eukaryotic signalling systems [ 16,50-52], detailed studies not only of their preparation but also of their structural analogues were undertaken by many laboratories. 

As the occurring short-lived intermediates (such as A-D and A -C, Scheme 1) occur on bismuthmolybdate surfaces, they are difficult to investigate or to identify directly, and at the end of the 1980s obviously a limit for the information available via investigations with the authentic catalysts was nearly reached [11]. However, the results of surface studies can represent an inspiration also for molecular chemists, and in the mid-1980s, the first molecular model compounds began to appear in the literature that had been prepared to support or dispute mechanistic postulates. Some accounts dealing with such model complexes have appeared already [11,15-17] the... 

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